This invention relates to fuel injection devices for spark ignition type internal combustion engines, and more particularly to fuel injection control devices for controlling the amount of fuel to be injected, synchronously and asynchronously with the crank angle signal, into the air inlet passage to the cylinders of internal combustion engines.
Conventionally, the supply of fuel to the spark ignition type internal combustion engines of passenger automobiles has been effected by carburetors; recently, however, fuel injectors are becoming increasingly common. These fuel injectors are capable of supplying a precisely controlled amount of fuel to the internal combustion engine so as to obtain an optimum air-fuel ratio. However, when the engine is in an accelerating transient state, the supply of fuel may be delayed with respect to the increase of the amount of air taken into the engine; this may be occasioned, for example, by: the delay of the detection of the amount of air intake; the delay in the calculation of the amount of fuel to be injected; and the delay resulting from the time which the fuel injected into the air intake pipes of the engine takes to reach the combustion rooms in the cylinders thereof. If the supply of fuel is thus delayed, the air-fuel ratio of the mixture supplied to the engine is deviated from the optimum level.
Thus, the accelerating state of the engine is detected by means of a parameter indicative of the operating state of the engine, so that a trasient accelerating augmentation of fuel is effected in accordance with such detection of the accelerating state of the engine. The acceleration state of the engine may be detected by means of the following state parameters: the opening degree of the throttle valve of the engine; the pressure of the intake air within the air inlet passage taken into the cylinders of the engine; and the amount of the intake air. Since the increment of these state parameters over an interval of time corresponds to the acceleration of the engine, the acceleration state of the engine can be determined by comparing the increment of a state parameter with a predetermined threshold level. The conventional fuel injection device, however, has the following disadvantage:
For the purpose of detecting a rapid acceleration of the engine with a quicker response speed, the interval of time over which the increment of the state parameter is calculated must be made shorter. On the other hand, for the purpose of detecting a slow acceleration of the engine with more enhanced sensitivity, the threshold level must be made lower; this is especially true when the interval of time over which the increment of the state parameter is calculated is short, since the magnitude of the increment during such short interval of time is small. However, the detection signal of the state parameter inevitably containes noises (i.e. small fluctuations of the detection signal which do not correspond to the actual variation of the state parameter); thus, the shorter the interval of time over which the increment is calculated, and the lower the threshold level with which the increment is compared, the more manifest are the adverse effects of the noises contained in the detection signal of the state paramter. Thus, the detection of the rapid acceleration of the engine with a quick response speed and the detection of the slow acceleration with enhanced sensitivity are two contradictory objects which cannot be accomplished simultaneously. Namely, if the rapid acceleration of the engine is to be detected quickly, the interval of time over which the increment is calculated must be made short; further, for the purpose of reducing the adverse efffects of the noises, the threshold level with which the increment is compared must be set high; this results in an inferior sensitivity of the detection of the slow acceleration. On the other hand, if the interval of time over which the increment is calculated is made longer for the purpose of detecting the slow acceleration without adverse effects of the noises, the response to the rapid acceleration becomes slower.